Results from our Rasch analysis led us to reduce the FS-C from 14 items to 10 items, thereby reducing the burden of time on children to complete the instrument and assessing only those items that best discriminated between patients who experienced high cancer-related fatigue and those who did not. Our confirmatory factor analysis revealed that the 10-item FS-C achieved acceptable internal consistency estimates, concurrent validity, and construct validity; thus, in its reduced form, the instrument was still a reliable and valid indicator of cancer-related fatigue in children.
By applying the ROC techniques to the 10-item FS-C, we identified the cut score of 12 with acceptable sensitivity (75%) and specificity (73.5%). This measure allowed us to distinguish children who had high cancer-related fatigue from those who did not. Our sensitivity and specificity values compared favorably with other ROC analyses in medical decision making.19–21
Furthermore, our AUC analysis yielded a strong finding of 0.768. Together, these results support the cut score of 12 on the FS-C and its ability to distinguish pediatric oncology patients with high cancer-related fatigue. The primary finding of this analysis is a clinically interpretable score of a child’s cancer-related fatigue. The cut-score can now be used by clinicians to guide their clinical assessments of this prevalent adverse effect of cancer and anticancer treatment. This score can also be used to signal the need to implement fatigue-directed treatment and to evaluate the effectiveness of that treatment.
The proportion of children who had cancer-related fatigue in our study sample suggests that fatigue in children with cancer differs in intensity by clinical context, i.e., approximately 33% of outpatients with diverse cancer diagnoses and those with ALL had high fatigue, and 40% of patients receiving chemotherapy as inpatients experienced fatigue at some point during their hospitalization. Furthermore, the proportion of hospitalized children with high fatigue tripled (from 12.5% to 38.9%) by the second night of hospitalization, and that proportion was maintained during the third night. The proportion of hospitalized children with high fatigue implies the need to routinely measure and treat, if necessary, fatigue in children with cancer during hospitalization for chemotherapy.
Certain limitations are apparent in this study. The independent criterion used to complete the ROC analysis was not a child-reported item or score but a parental report. The parent diary item is a well-tested item from an instrument that has been validated using objective child actigraphy scores.11
Proxy ratings are the standard in other medical decision-making studies that use the ROC analysis; thus, our use is similar to that of one or more items from family members or health care professionals as the independent criterion in these other studies. An additional limitation of this study is the lack of a validation sample to further assess the ROC technique with the FS-C and the Daily Sleep Diary–Parent. We plan to include this comparison in our future studies.
Assessing the cut score validation samples that reflect diverse clinical contexts will help confirm the cut score and further study the influence of context on the proportions of patients at risk for high fatigue. As interventions for cancer-related fatigue evolve, consideration of a scoring system to identify a range of fatigue scores (i.e., low, moderate, and high) will also need to be developed. After those ranges have been identified, the feasibility, fit, and effectiveness of interventions for each intensity range will need to be tested. As strong clinical correlates of fatigue are confirmed over time, their use in the ROC as the gold standard of comparison, against the patient-reported fatigue, will also be important to assess and compare with that of the parental perspective.